Dark matter as matter in parallel universes

[Chalnoth]

Chalnoth, I understand that dark matter shows no sign of gravitational interaction even with itself, but, as I said in my previous post, in my cosmology, that can be because bits of it aren't really as close as they they seem in the LQG hyperspace.

Presumably you meant non-gravitational interaction. But then, if the dark matter wasn't that close to itself, it wouldn't be close to us either, and thus we wouldn't feel its effects very much.

 

[Misericorde]

It doesn't exactly bowl me over than a name from Star Trek would be something you find cropping up in more than one forum related to science in general.

I keep hearing in this thread about dark matter as a product of universes other than our own, but even if possible (and twofish-quant has made that sensible), doesn't Occam's Razor cut far too close for that? I'd want to see native matter eliminated through process and trial before looking to other realities.

 

[DavidMcC]

It doesn't exactly bowl me over than a name from Star Trek would be something you find cropping up in more than one forum related to science in general.

I keep hearing in this thread about dark matter as a product of universes other than our own, but even if possible (and twofish-quant has made that sensible), doesn't Occam's Razor cut far too close for that? I'd want to see native matter eliminated through process and trial before looking to other realities.

I don't see how "Occam's razor" can be defeat the right kind of multiverse - on the contrary. The problem of conventional, one big bang cosmology are very severe, in that nothing makes sense. Dark matter is but one little aspect of it. Slight parity violation in particle physics, the appearance of fine tuning of the universe for life (the values of the fine structure constant and strong interaction), the variability of the cosmological "constant", inflation, are all better explained by the right kind of multiverse (ie a "fecund universe" type once proposed by Smolin, but I don't want to go through that yet again, there are now so many threads on this , it gets tiresome). I suspect two things : (1) Smolin was too soon with this hypothesis, so that there wasn't enough evidence for it at the time, and (2) there were many rubbish versions of the multiverse, which do, indeed, just complicate things.
EDIT: Also, a single big bang is highly improbable if big bangs are a natural process. Therefore, we only DETECT one with light - the one we're in.

 

[Chalnoth]

I don't see how "Occam's razor" can be defeat the right kind of multiverse - on the contrary.

Yes, Occam's Razor actually prefers a multiverse, even if we don't look at any data. This simply comes down to the fact that within mathematics, it is much easier to get a class of objects than it is to get a single member of that class. So it is a unique universe, not a multiverse, that needs evidence to support it. And the fact is that all of the evidence that has any relevance to this question at all so far points more to a multiverse than it does to a unique universe.

 

[Misericorde]

Let me rephrase: the notion of an infinite number of universes is not subject to Occam's Razor if you believe in eternal inflation, or a multiverse of many isolated pockets. It does cut finely (I think) in the case of QM interpretations such as MWI where it's just another variable to remove the "artifact" of collapse.

 

[Chalnoth]

It does cut finely (I think) in the case of QM interpretations such as MWI where it's just another variable to remove the "artifact" of collapse.

In the MWI, there are actually fewer assumptions than in other interpretations. The MWI just assumes the wavefunction dynamics of quantum mechanics, full stop. Other interpretations assume some sort of collapse or other mechanism that looks like collapse. MWI just looks at the wavefunction dynamics and notes that the appearance of collapse is already there, no extra bells and whistles required.

This is just one example (among many) of why a multiverse is preferred over a unique universe.

 

[twofish-quant]

In the interest of relating everything to observations, let me point out that a lot of the interest in parallel universes was inspired by recent observations of extra solar planets. It turns out that when we look at extra solar planets, that hot jupiters are very common, but we don't see them in our own solar system, which makes people wonder why our solar system seems to be specially tuned for life, and of course the answer is obvious. If our solar system had a hot jupiter, we wouldn't be here, and it turns out that the orbits of Jupiter and Saturn are specially tuned so that they are well-behaved...

The other problem is that it turns out that in standard particle physics theories none of the fundamental constants are uniquely determined. The value of the fine structure constant at "zero energy" happens to be because the universe settled at this energy state after symmetry breaking happened.

So this got people thinking about how this applies to the whole universe. I know one scientist that wrote a critical paper on the possibility of multi-universes and he mentions this explicitly as one of the things that got him thinking about it.

 

[DavidMcC]

Twofish-quant, I thought all the other observational reasons for suspecting a multiverse are actually rather more convincing than mere exoplanet tendencies, which have nothing much to do with the issue, as far as I'm concerned.
However, I agree about your second para.

 

[Misericorde]

MWI has fewer than other interpretations except the only one that has any evidence to support it: shut up and calculate. I don't understand why people think they're going to form a valid ontology based on a theory which is not a "final" theory. Occam's Razor cuts closer to the bone than an attempt to rationalize why we don't recognize quantum behaviour in everyday life (dead/alive cats).

I'd add, if we're going to be willing to boil everything down to imponderables such as "before" the BB, or an infinite multiverse, eternal inflation, and so on... well... why not just say that this universe is all that there is, period. What's outside of the universe? Well, it's possibly as salient as asking for a before the BB; it's just not something human beings can contemplate; eternity, nothingness, a lack of time.

We wisely ignore those issues as being beyond the scope of physics, or at least not falsifiable or verifiable, right? Well, my view is that using the data we have now to even wonder about the 'why' of our existence and the ability of a universe or multiverse to support wondering organisms is predicated on failure. We have imperfect theories, but the benefit of them is the technology and progress they allow; I suppose if a final theory were developed then moving on to ontology would make sense, but right now it's hubris.

 

[DavidMcC]

Presumably you meant non-gravitational interaction. But then, if the dark matter wasn't that close to itself, it wouldn't be close to us either, and thus we wouldn't feel its effects very much.

It's a tricky point, Chalnoth. Maybe gravity simply has a short range in hyperspace, so we only feel the gravity from those bits that are very close in it, and by the same token, those bits are isolated from each other.

 

[Chalnoth]

It turns out that when we look at extra solar planets, that hot jupiters are very common, but we don't see them in our own solar system, which makes people wonder why our solar system seems to be specially tuned for life, and of course the answer is obvious.

Well, the difficulty here is that this is almost certainly a selection effect. Hot Jupiters have high masses and short orbital periods, and so are the easiest to observe. The fact that we see a lot of them seems to indicate more that planets in general are likely to be very common. In fact, given that within our own solar system, every one of the more massive planets has a plethora of moons argues rather strongly that nearly every star out there will similarly have a number of planets (though obviously the more violent star systems, such as, say, tight-orbiting binaries, may end up destroying any planets that form).

If our solar system had a hot jupiter, we wouldn't be here, and it turns out that the orbits of Jupiter and Saturn are specially tuned so that they are well-behaved...

Well, Jupiter and Saturn couldn't exist if their orbits weren't well-behaved, because our solar system is some 4.5 billion years old. Anything that wasn't well-behaved that was that massive would have collided with something over the billions of years our solar system has been around.

 

[Chalnoth]

It's a tricky point, Chalnoth. Maybe gravity simply has a short range in hyperspace, so we only feel the gravity from those bits that are very close in it, and by the same token, those bits are isolated from each other.

That doesn't help.

And by the way, in order to explain our own observations of gravity, gravity in a higher-dimensional space would have to be stronger than it is in our 3+1 dimensions, not weaker.

 

[Chalnoth]

MWI has fewer than other interpretations except the only one that has any evidence to support it: shut up and calculate.

You mean the Copenhagen interpretation? Sorry, but that one has been falsified by observations of quantum decoherence.

 

[Misericorde]

You mean the Copenhagen interpretation? Sorry, but that one has been falsified by observations of quantum decoherence.

I mean exactly what I said: "shut up and calculate", not worry about collapse unless decoherence is the focus on your study. The solution to a falsified theory is not to invent countless interpretations of a theory, a majority of which are not falsifiable even if they are elegant. The solution is to calculate and work toward a greater understanding of what is right and wrong in the current formulation, observing and recording, and creating a NEW THEORY.

Clearly GR and QM have holes in them, but they also predict nature with astonishing fidelity. To assume that doesn't mean we have an infinite series of half-steps to a final theory however, again, seems like hubris. Shut up and calculate, and fine tune until we get so close it makes no difference, or we're all dust. It's good to identify the ontological problems uncovered, and some areas such as DCQE experiments demand explanation. I do not believe that interpretation of existing theories is of value in finding that however, but rather only new theories which are MORE predictive and explanatory. The rest is very admirable, but still very clearly intellectual masturbation.

 

[Chalnoth]

I mean exactly what I said: "shut up and calculate", not worry about collapse unless decoherence is the focus on your study. The solution to a falsified theory is not to invent countless interpretations of a theory, a majority of which are not falsifiable even if they are elegant. The solution is to calculate and work toward a greater understanding of what is right and wrong in the current formulation, observing and recording, and creating a NEW THEORY.

Sounds like a hand-wavy excuse to stop thinking about it to me.

My entire point was that absent evidence to discern which way to go, we should always consider the explanation with the fewest assumptions to be the most likely. That's MWI. And it turns out that this has been confirmed by observations of quantum decoherence. To claim that there is still some "real" collapse besides simple decoherence is an unjustified and unjustifiable claim and should be considered nonsensical.

 

[Misericorde]

Sounds like a hand-wavy excuse to stop thinking about it to me.

My entire point was that absent evidence to discern which way to go, we should always consider the explanation with the fewest assumptions to be the most likely. That's MWI. And it turns out that this has been confirmed by observations of quantum decoherence. To claim that there is still some "real" collapse besides simple decoherence is an unjustified and unjustifiable claim and should be considered nonsensical.

There's nothing at all wrong with thinking about it, but there's thinking about it, and forming armed camps; I see far more of the latter.

 

[twofish-quant]

There's nothing at all wrong with thinking about it, but there's thinking about it, and forming armed camps; I see far more of the latter.

The problem is that without any observational tests, then a lot depends on personal impressions which can be different from person to person. If person A thinks that MWI is simplier or more elegant than Cophenhagen and person B disagrees, there is really no way of resolving this argument. I think that Picasso is more elegant than Rembrandt, and you disagree. There is just no way of convincing each other.

The other problem is that Ockham's razor is a heuristic. Heuristics can be wrong. Also, you get into the issue of fewest assumptions. To argue that there is this other world in which I'm now shopping at a computer mall rather than typing in a computer, is just weird. Not to say that it's wrong, but it's weird.

Also, this is why some people (like myself) stay away from the whole argument is quantum interpretation. It's like listening to people debate religion. If you can figure out a way to come up with an experiment that shows that the Wisconsin Lutherans are right and the Missouri Luthereans are wrong or vice versa, then I'm interested, but otherwise I tend to tune out. If instead of talking about experimental data, we are using simplicity and elegance as determining factors for truth, then we are in the world of religion and fashion. Not that this is a bad thing, but it's something that I'm not personally interested in.

Having said that it turns out that people *have* suggested a very simple experiment that I can do that can confirm that MWI is correct. Google for quantum suicide. The cool thing about that experiment is that it will happen naturally anyway so if the quantum immortality people turn out to be right, I'll know about it in a few decades anyway. No need to rush things.

Finally, one other reason I personally don't think too much about this sort of thing is that I do sometimes worry about losing my grip on reality.

One really weird idea that I'd like to throw out as a question for someone else to work on the math. Suppose the MWI is correct and at every moment the universe is making multiple copies of itself. Also let's assume that that in all of those universes the laws of physics are not fixed. So that right now there are an infinite number of multiple universes forming with a different value of the fine structure constant. Now if the fine structure constant or the gravitational constant suddenly changed, I die. So at every moment, there is are infinite number of alternative universes forming and in all but a small fraction of them, I die. Now using some statistics, I ought to be able to come up with some statements about what I'm likely to observe. For example, there are going to be limits on how fast I observe Planck's constant or the fine structure constant changing, because if it changes too fast, I die. So at every moment, massive multiple copies of me are forming and dying, I ought to be able to figure this out by looking at some statistics.

 

[Chalnoth]

Having said that it turns out that people *have* suggested a very simple experiment that I can do that can confirm that MWI is correct. Google for quantum suicide. The cool thing about that experiment is that it will happen naturally anyway so if the quantum immortality people turn out to be right, I'll know about it in a few decades anyway. No need to rush things.

The main problem is that the whole thought experiment assumes that there is a stark dividing line between consciousness and death. In reality even the most violent of deaths turn out to be pretty gradual compared to the electromagnetic interactions that cause decoherence. Death is actually a gradual disintegration of consciousness compared to those interactions, and thus behaves quite classically.

This gradual disintegration of consciousness destroys the thought experiment because instead of a dead/alive situation, it's one of slightly less conscious vs. slightly more conscious with each step of decoherence, so that there isn't any selection effect keeping people conscious. And by the time the instant of death comes, your consciousness is already so fragmented that there still isn't any selection effect going on.

So there really isn't any reason to worry about quantum indeterminacy causing immortality.

One really weird idea that I'd like to throw out as a question for someone else to work on the math. Suppose the MWI is correct and at every moment the universe is making multiple copies of itself. Also let's assume that that in all of those universes the laws of physics are not fixed. So that right now there are an infinite number of multiple universes forming with a different value of the fine structure constant. Now if the fine structure constant or the gravitational constant suddenly changed, I die. So at every moment, there is are infinite number of alternative universes forming and in all but a small fraction of them, I die. Now using some statistics, I ought to be able to come up with some statements about what I'm likely to observe. For example, there are going to be limits on how fast I observe Planck's constant or the fine structure constant changing, because if it changes too fast, I die. So at every moment, massive multiple copies of me are forming and dying, I ought to be able to figure this out by looking at some statistics.

Well, this doesn't apply to reality, however, because such changes in the laws of physics couldn't be global changes, so that if they happened with any frequency, we'd see them happening elsewhere in the universe. We don't, so it's wrong. Whatever determines the low-energy laws of physics must make them stable enough that we wouldn't have observed any change in them for the history of the observable universe.

 

[Lost in Space]

Regarding the quantum immortality thing, doesn't it all really boil down into whether things are infinitely probabilistic (speculatively speaking of course)? How many chances in infinity would it necessitate to be immortal in one or more universes? Isn't the chance one in infinity? If one was immortal in more than one universe, would one still be one? Shouldn't decoherence ultimately resolve the paradox down to a single factor where, if at all possible, one could only be immortal in one universe?

 

[twofish-quant]

Death is actually a gradual disintegration of consciousness compared to those interactions, and thus behaves quite classically.

Yes, I know. That's why I haven't done the experiment. :-) :-) :-)

The problem with the argument is that even if death "normally" comes classically, with some cleverness you could set up a situation in which death comes quantum mechanically. You need to have something happen so quickly, that my brain vaporizes on the order of the decoherence time.

But it would be a bummer to get the experiment wrong.

So there really isn't any reason to worry about quantum indeterminacy causing immortality.

I think there is. The problem is that we don't know very much about the physics of consciousness. I think Penrose is a nut, but if there is something inherently quantum mechanical about consciousness, then this will impact the whole idea.

Well, this doesn't apply to reality, however, because such changes in the laws of physics couldn't be global changes, so that if they happened with any frequency, we'd see them happening elsewhere in the universe.

What would it look like if the fine structure constant suddenly changed to 1 or 1/1000 in some part of the universe? If it causes some effect that would either kill me or set create a situation in which I'd never come to being in the first place, then in the universes where parts of the universe do suddenly change physical constants, I'm dead.

Now if the fine structure constant changes by 1e-20, then I don't die. However, if you look at how much the fine structure constant has to change before I die, you'd come up with some limits as to where and how the FSC can change, and it will be interesting to see what they are.

Whatever determines the low-energy laws of physics must make them stable enough that we wouldn't have observed any change in them for the history of the observable universe.

If the laws of physics changed sufficiently much, then intelligent life would be impossible. One calculation that could be done is to what are the limits of changes of laws of physics that would be consistent with the development of life. This has the good affect of taking anthropic arguments out of the unobservable multiverse and putting it into the universe.

If you find that you have have large changes in the laws of physics and still have intelligent life, then anthropic arguments are not going to work, but that also kills anthropic arguments for parallel universes. If on the other hand, you come up with arguments that the fine structure constant can only change so much for life to exist, then it gets interesting.

What would be really interesting is if you find that the limit for the change of the FSC is something like 1e-10/year, and then you find that the FSC *is* changing at some fraction of that.

On the subject of weird ideas. One thing that occurs to me is if the universe is totally classical, then intelligence would be impossible. The future would be determined, and the ability to think of alternative futures and to act on them would be useless since there is only one possible future. Alternatively, if the universe were totally random, intelligence would also be impossible. So the universe has to be just random enough so that you can have some choice in your actions, but not so totally random as to make prediction of the future impossible.

One thing I've been trying to figure out is what is the value of the fine structure constant that would give you "just enough randomness" for intelligence to development.

 

[Misericorde]

The problem is that without any observational tests, then a lot depends on personal impressions which can be different from person to person. If person A thinks that MWI is simplier or more elegant than Cophenhagen and person B disagrees, there is really no way of resolving this argument. I think that Picasso is more elegant than Rembrandt, and you disagree. There is just no way of convincing each other.

Yeah, and that's art, not physics which should be an empirical endeavor and not an argument over taste. The issue isn't believing in collapse, or MWI, or anything else... just work the equations; that's what SUAC is! Metaphysics is plenty of fun, but it's become this serious endeavor on par with actual research. The same experiments will be run regardless, energy levels and temperatures will rise, new observations will be made, and theories will change. None of that is going to materially interact with the artistic preferences of the scientists involved; surely Einstein's own bias is proof enough of that.

The other problem is that Ockham's razor is a heuristic. Heuristics can be wrong. Also, you get into the issue of fewest assumptions. To argue that there is this other world in which I'm now shopping at a computer mall rather than typing in a computer, is just weird. Not to say that it's wrong, but it's weird.

That's true, but I don't see the relevance; it's a far more proven tool than the others which can also be wrong which are employed to create fanciful interpretations without adding to the physics.

Also, this is why some people (like myself) stay away from the whole argument is quantum interpretation. It's like listening to people debate religion. If you can figure out a way to come up with an experiment that shows that the Wisconsin Lutherans are right and the Missouri Luthereans are wrong or vice versa, then I'm interested, but otherwise I tend to tune out. If instead of talking about experimental data, we are using simplicity and elegance as determining factors for truth, then we are in the world of religion and fashion. Not that this is a bad thing, but it's something that I'm not personally interested in.

Yeah, that's why I advocate SUAC (Shut Up And Calculate), because that's physics, rather than putting a spin on why a certain calculation is done.

Having said that it turns out that people *have* suggested a very simple experiment that I can do that can confirm that MWI is correct. Google for quantum suicide. The cool thing about that experiment is that it will happen naturally anyway so if the quantum immortality people turn out to be right, I'll know about it in a few decades anyway. No need to rush things.

I'm familiar with this, I agree with Chalnoth, and like you have no desire to rush that particular experiment. Besides, on a serious note, death appears to be an event horizon for us; we don't get to report back if there's something on the other side, and we don't see anything from this end.

Finally, one other reason I personally don't think too much about this sort of thing is that I do sometimes worry about losing my grip on reality.

In a fit of irony, it's this "head trip" that I think people most want from interpretations of QM. In a limited sense as a teaching tool, it can help to break the desire for an intuitive model of nature, but as an ongoing and constant exploration it basically becomes mysticism.

One really weird idea that I'd like to throw out as a question for someone else to work on the math. Suppose the MWI is correct and at every moment the universe is making multiple copies of itself. Also let's assume that that in all of those universes the laws of physics are not fixed. So that right now there are an infinite number of multiple universes forming with a different value of the fine structure constant. Now if the fine structure constant or the gravitational constant suddenly changed, I die. So at every moment, there is are infinite number of alternative universes forming and in all but a small fraction of them, I die. Now using some statistics, I ought to be able to come up with some statements about what I'm likely to observe. For example, there are going to be limits on how fast I observe Planck's constant or the fine structure constant changing, because if it changes too fast, I die. So at every moment, massive multiple copies of me are forming and dying, I ought to be able to figure this out by looking at some statistics.

...And just like that you sent me to the research block for about 2 hours! Thanks for giving me an opportunity to learn, and realize the magnitude of the challenge you're setting there. Let's hope for a genius with an answer in our lifetimes, because it's not going to be us! ;)

 

[Misericorde]

I'd add the quantum suicide issue, that until I have some assurance that dying, or for a more local example, being teleported Star Trek style isn't the same as dying and being replicated, I'll pass. If dualists are right, there are some serious questions, and if materialists are right, there are still serious questions. Am I traveling, or just being cloned at a remote location, and what does that mean to the 'me' writing this? This is either a question with an answer, or the kind of thing that as twofish-quant so rightly said, can detach one from reality. Physics problems that are predicated on understanding the nature of life, death, and the seat of consciousness strikes me as trying to understand why balls bounce by first having to explain the BB.

 

[twofish-quant]

Regarding the quantum immortality thing, doesn't it all really boil down into whether things are infinitely probabilistic (speculatively speaking of course)?

Don't know. The reason the quantum immortality thing is interesting is that it's the only experiment that I know of that even *in principle* could tell the different between MWI and Copenhagen. Even if it doesn't work, it's a nice try, and if you think about it long enough you might come up with something else. Or not.

One other interesting part of parallel universes are the theological implications. If you look at the Medieval glass windows, you have heaven in the clouds and hell in the center of the earth. Well heaven isn't physically in the clouds, since I've been up there with an airplane and I didn't see any pearly gates.

However, once you have the idea of parallel universes, then you can find a place for heaven and hell to physically exist. Also, if you have a situation in which the parallel universes can interact, then you have room for all sorts of interesting theology.

Now I can't really work on this because I've been exposed to too many religious traditions to have a deep belief in any of them. But it's only a matter of time before someone like Hugh Ross or Robert Jastrow or Guy Consolmagno starts running with these ideas. Frank Tipler has already gone down that route and most people think that he has lost it. David Deutsch has also been thinking about these sorts of things. Will be interesting to see what comes out.

How many chances in infinity would it necessitate to be immortal in one or more universes? Isn't the chance one in infinity? If one was immortal in more than one universe, would one still be one? Shouldn't decoherence ultimately resolve the paradox down to a single factor where, if at all possible, one could only be immortal in one universe?

You know that you have an interesting idea when it causes you to ask interesting questions.

 

[Chalnoth]

Yes, I know. That's why I haven't done the experiment. :-) :-) :-)

The problem with the argument is that even if death "normally" comes classically, with some cleverness you could set up a situation in which death comes quantum mechanically. You need to have something happen so quickly, that my brain vaporizes on the order of the decoherence time.

But it would be a bummer to get the experiment wrong.

I just don't think that's possible.

I think there is. The problem is that we don't know very much about the physics of consciousness. I think Penrose is a nut, but if there is something inherently quantum mechanical about consciousness, then this will impact the whole idea.

We know everything we need to know as far as quantum mechanics is concerned: individual cells behave almost entirely classically.

What would it look like if the fine structure constant suddenly changed to 1 or 1/1000 in some part of the universe? If it causes some effect that would either kill me or set create a situation in which I'd never come to being in the first place, then in the universes where parts of the universe do suddenly change physical constants, I'm dead.

As long as it's far away, then it most definitely won't kill you. But it will do things like dramatically change the properties of stars, or cause massive explosions. Changing the fine structure constant also changes the distribution of spectral lines, so galaxy spectra would look completely crazy with unidentifiable spectral lines.

The main point here is that we can definitely assume that causality holds so that if there is a change in something like the fine structure constant, that change will start at some specific location in the universe and propagate outward. As long as it does so slower than the speed of light (even slightly), then we will see it happening before it reaches us. And because our universe is so incredibly big while such an event could have happened anywhere, it is quite unlikely that such events happen with any noticeable frequency.

Now if the fine structure constant changes by 1e-20, then I don't die. However, if you look at how much the fine structure constant has to change before I die, you'd come up with some limits as to where and how the FSC can change, and it will be interesting to see what they are.

Current limits are to within a couple percent, if I remember correctly, out to the emission of the CMB.

 

[twofish-quant]

I just don't think that's possible.

You give up too easily.

One thing that also occurs to me is what happens if there is a sudden loss of consciousness. I go in for an operation, and they put me under, and my consciousness is zero. In one world, a cosmic ray causes the surgeon to mess up and I die on the table and never wake up. In another world, everything goes fine.

So what do I experience?

We know everything we need to know as far as quantum mechanics is concerned: individual cells behave almost entirely classically.

Almost entirely != entirely.

Also we do not know how cell activity gives rise to consciousness. One thing that bothers me is that I go to sleep at night. I lose consciousness, in the morning I wake up, and I'm not someone else (or am I?) That's always bothered me.

As long as it's far away, then it most definitely won't kill you.

If it's far away then it happened in the past, and if it happened in the past, then it likely kept me from existing in the first place.

The main point here is that we can definitely assume that causality holds so that if there is a change in something like the fine structure constant, that change will start at some specific location in the universe and propagate outward.

Why should we assume that causality holds? What could be happening is that MWI causes vast number of acausal universes to come into being, but I don't notice any of them, because consciousness requires causality to function, and in the acausal universes, I cease to exist.

One interesting paper by Tegmark argues that anthropically the universe must be 3+1, because if you have a different number of dimensions, causality doesn't mathematically work. If the number of dimensions in the universe changes, I cease to exist. If time starts going backward, I cease to exist.

The reason I'm thinking along these lines is that if you take the rules of QFT and just turn it sideways, you get the rules of statistical mechanics. That's interesting. Statistics of what?

As long as it does so slower than the speed of light (even slightly), then we will see it happening before it reaches us.

But these hypothetical changes are happening at Planck's timescale. And for you to notice anything requires some fine tuning. If the change hits you before you were born, then you wouldn't exist.

Also suppose you are right. Then even then you have some very interesting implications. You have a huge number of universes generated by the MWI, but the FSC and Planck's constant is the same in all of them.

And because our universe is so incredibly big while such an event could have happened anywhere, it is quite unlikely that such events happen with any noticeable frequency.

Our universe isn't that big. Also, right now we are in the realm of gut feeling, and I'd like to get numbers.

Let me tell you one reason why I find the concept of parallel worlds weird.

Suppose you have a benevolent, hyperintelligent being named Fred. Now suppose Fred likes me. Fred is likes me enough so that Fred is annoyed that I end up dying so he wants to do something about that. So Fred takes some matter and randomly rearranges it. You can calculate how long it will take before that random matter ends up with me. Now if you have one universe, the stars will burn out and the universe will suffer heat death before that happens.

However, let's assume that MWI is right and you have multiple universes. In each universe Fred randomally rearranges atoms. You can mathematically show that in those universes, I'm going to pop out. Fred is systematically going through all combinations of organic molecules, and in one of them, I'm going to come out of the machine.

OK. Someone else is going to work out the theological implications. But my point is that if you accept MWI as true then you expand the universe enough so that in one of the universes Fred is wandering around with pearly gates and being with wings and halos reserruecting people from the dead.

Curiously, I don't like to think about this sort of stuff for vary long because it messes with my mind a lot. If I think about Italian food or Android apps, I can tell the difference between crackpot and non-crackpot. If I spend too much time thinking about quantum mechanics, I can't tell the difference.

BTW, right now I'm working on an Android app that creates alternative universes. The idea is that I have my cell phone do some sort of quantum mechanical process that has a 50-50 chance of going in either direction. So any time I need to make a decision, I press the button on my cell phone, and it rolls the dice and I order potato salad rather than lima beans. However, because the random factor is a QM process, then if MWI is right then in some other world, the phone rolled the dice in a different way, and I ordered lima beans instead of potato salad.

Right now, the hard part is trying to come up with a quantum process that you can put on a phone. It's actually less hard than it sounds because people are interested in using random processes to general cryptographically secure keys.

 

[Chalnoth]

You give up too easily.

One thing that also occurs to me is what happens if there is a sudden loss of consciousness. I go in for an operation, and they put me under, and my consciousness is zero. In one world, a cosmic ray causes the surgeon to mess up and I die on the table and never wake up. In another world, everything goes fine.

So what do I experience?

Eh, I suppose that might fit the thought experiment. But that is extraordinarily contrived, and not at all a situation that anybody experiences, at least not to a degree that makes any sort of difference to anybody.

Almost entirely != entirely.

Also we do not know how cell activity gives rise to consciousness. One thing that bothers me is that I go to sleep at night. I lose consciousness, in the morning I wake up, and I'm not someone else (or am I?) That's always bothered me.

What we do know, however, is that consciousness arises through the collective action of large numbers of neurons. That collective action is guaranteed to make the system even more classical.

If it's far away then it happened in the past, and if it happened in the past, then it likely kept me from existing in the first place.

Again, speed of light. Such a change cannot propagate faster, and would most likely propagate slower.

Why should we assume that causality holds?

It holds within our space-time. The speed of light may be different within the new region generated by the change in the fundamental laws, but that can't affect things until the region expands.

What could be happening is that MWI causes vast number of acausal universes to come into being, but I don't notice any of them, because consciousness requires causality to function, and in the acausal universes, I cease to exist.

Well, there is actually some work that is sort of kinda similar to this, in that only certain subsets of the full quantum wavefunction are stable.

Our universe isn't that big. Also, right now we are in the realm of gut feeling, and I'd like to get numbers.

It is for the purpose of this kind of thought experiment.

Let me tell you one reason why I find the concept of parallel worlds weird.

Lots and lots of things about modern physics are weird.

Suppose you have a benevolent, hyperintelligent being named Fred. Now suppose Fred likes me. Fred is likes me enough so that Fred is annoyed that I end up dying so he wants to do something about that. So Fred takes some matter and randomly rearranges it. You can calculate how long it will take before that random matter ends up with me. Now if you have one universe, the stars will burn out and the universe will suffer heat death before that happens.

However, let's assume that MWI is right and you have multiple universes. In each universe Fred randomally rearranges atoms. You can mathematically show that in those universes, I'm going to pop out. Fred is systematically going through all combinations of organic molecules, and in one of them, I'm going to come out of the machine.

Well, yeah, but the number of worlds where you don't pop out is so unbelievably numerous compared to the number of worlds where you do that Fred would have to be positively insane to bother.

OK. Someone else is going to work out the theological implications. But my point is that if you accept MWI as true then you expand the universe enough so that in one of the universes Fred is wandering around with pearly gates and being with wings and halos reserruecting people from the dead.

Well, no, because MWI only predicts that all possible outcomes occur. We can imagine plenty of things that aren't possible, and don't even yet know how to describe all of what is and is not possible.

 

[twofish-quant]

Eh, I suppose that might fit the thought experiment. But that is extraordinarily contrived, and not at all a situation that anybody experiences, at least not to a degree that makes any sort of difference to anybody.

Ummmm... I don't think it's very contrived.

At some point in my life, there is a very good chance that I will go into surgery with zero consciousness under some situation in which there is a good chance that I won't make it through do to quantum events.

In fact, the fact that I'm going to find out what happens soon enough is why I'm not in a hurry to do the experiment. Also, "what does it feel like to die?" is something that makes a great difference to a lot of people.

What we do know, however, is that consciousness arises through the collective action of large numbers of neurons. That collective action is guaranteed to make the system even more classical.

Not necessarily. Superconductors are a good example in which collective action of large numbers of atoms makes the system *less* classical. Ferromagnetism is another example where large numbers of atoms makes the system *less* classical. There are probably a dozen other examples that condensed matter people can come up with. You can argue that those aren't directly relevant, and I think you would be right, but they are examples where you can't just say "lots of moving parts -> more classical". In those examples "lots of moving parts -> less classical."

Well, yeah, but the number of worlds where you don't pop out is so unbelievably numerous compared to the number of worlds where you do that Fred would have to be positively insane to bother.

Fred loves me a lot. Also if you are in a situation in which psychological arguments are considered valid, then you are pretty firmly in the realm of theologists.

Well, no, because MWI only predicts that all possible outcomes occur.

And what's impossible about a hyperintelligent being with pearly gates and angels? Think of it as a parallel universe mega-Disneyland. Doesn't violate any law of physics I can see.

The thing about MWI, is that if you assume there is only one universe, then most possible things will not occur. If you have MWI, then anything that is possible will occur, and I just have to show that creating a parallel universe mega-Disneyland with fun rides for people that have been good isn't physically impossible and it will happen.

This matters because the barriers against raising the dead are thermodynamic and there are no really physics barriers against "practical immortality." Once you have MWI, you there are thermodynamic implications.

We can imagine plenty of things that aren't possible, and don't even yet know how to describe all of what is and is not possible.

However, if you have parallel universes, you remove a lot of the computational restrictions on what is possible. For example, if I give you a 1024-bit number it may well be mathematically impossible to factor before the universe suffers heat death. If you have MWI, then it's trivial to show that in some universe, someone will successfully factor that number, and in fact people are using that fact for quantum cryptography.

You have a nanobot create an android and then through some quantum process, run through all possible memories for that android.

Again, this isn't to say that MWI is right or wrong. But I think you can very much argue that if MWI is right then a lot of interesting conclusions follow.

 

[Chalnoth]

Ummmm... I don't think it's very contrived.

At some point in my life, there is a very good chance that I will go into surgery with zero consciousness under some situation in which there is a good chance that I won't make it through do to quantum events.

Um, it's extraordinarily unlikely that you'll find yourself in a situation where you are unconscious and your life or death will depend upon quantum events. Remember that the regime at which quantum effects are important is extremely low temperatures or very small systems (on the order of hundreds of atoms). Because of this, the system would have to be explicitly set up to depend upon measurements of a carefully-prepared quantum system. So yes, extremely contrived and not applicable to reality.

Not necessarily. Superconductors are a good example in which collective action of large numbers of atoms makes the system *less* classical. Ferromagnetism is another example where large numbers of atoms makes the system *less* classical. There are probably a dozen other examples that condensed matter people can come up with. You can argue that those aren't directly relevant, and I think you would be right, but they are examples where you can't just say "lots of moving parts -> more classical". In those examples "lots of moving parts -> less classical."

Not in the sense of quantum superpositions being an important aspect of the phenomena, which is all that is relevant for this kind of issue.

Fred loves me a lot. Also if you are in a situation in which psychological arguments are considered valid, then you are pretty firmly in the realm of theologists.

Uh, what?

The thing about MWI, is that if you assume there is only one universe, then most possible things will not occur. If you have MWI, then anything that is possible will occur, and I just have to show that creating a parallel universe mega-Disneyland with fun rides for people that have been good isn't physically impossible and it will happen.

This matters because the barriers against raising the dead are thermodynamic and there are no really physics barriers against "practical immortality." Once you have MWI, you there are thermodynamic implications.

This kind of objection doesn't make any sense. Probabilities within MWI strictly adhere to the Born Rule, so even if you can suppose that some seemingly weird thing might exist, the probability of you finding yourself in that world is so unbelievably minuscule that it is irrelevant.

 

[twofish-quant]

Um, it's extraordinarily unlikely that you'll find yourself in a situation where you are unconscious and your life or death will depend upon quantum events. Remember that the regime at which quantum effects are important is extremely low temperatures or very small systems (on the order of hundreds of atoms).

Very strongly disagree.

http://en.wikipedia.org/wiki/Hardware_random_number_generator

Shot noise is a quantum phenomenon, and you can imagine a situation in which a resistor that is near tolerance fails or doesn't fail due to the current flow. For that matter you can have a situation in which a resistor fails or doesn't fail because a cosmic ray does or doesn't hit a critical item. The reason I'm under the knife in the first place may be because I was near a piece of uranium that did or did not emit an alpha particle that did or did not knock out a critical piece of DNA, that did or did not cause things to be cancerous.

Because of this, the system would have to be explicitly set up to depend upon measurements of a carefully-prepared quantum system. So yes, extremely contrived and not applicable to reality.

Not hard. Happens all of the time. You have a resistor that is about to burn out. The shot noise either puts the current over or under the limit. In one universe, it goes over, resistor burns out. Distracts the surgeon, I die.

Also it's not hard to make it happen. That's the cool thing about the Android app that I'm working on. I use a hardware random number generator to flip a coin based on quantum principles. In one universe, I go to the park and nothing happens. In another universe, I end up in a busy intersection where I get hit by a bus.

This isn't a hard experiment.

Not in the sense of quantum superpositions being an important aspect of the phenomena, which is all that is relevant for this kind of issue.

The problem here is that if you accept MWI, the wave function is *always* in a state of superposition. With Copenhagen and anything else, the wave functions collapses, the superposition disappears. With MWI, the superposition *doesn't* disappear after you do the measurement. It's just that the outcome of that measurement are in different universes which you don't notice.

So if you accept MWI, quantum superpositions are always important because they don't disappear after you do the experiment.

Part of the problem here is that the talk of quantum consciousness has been dominated by Roger Penrose, and it's pretty easy to show that his ideas are wrong. But superposition is not the only quantum effect, and even thought the electrons in my computer or a laser are nicely collapsed, quantum effects are important in both of them.

The reason this matters is that there is one missing part of MWI which is the fact that I don't feel the universe splitting. I hit my hardware random number generator. It tells me to eat steak instead of salmon, but MWI says that somewhere else there is a different me that got told to eat salmon instead of steak. Quantum suicide and immortality are ideas that try to figure out what is going on. They might be wrong, but it's not an issue that is irrelevant, and you just can't around the problem by doing what you are doing by saying that the problem doesn't matter.

I seriously doubt that my brain doesn't have some quantum noise in it, but since I'm not a neuroscientist, let's say that you are right and my brain is completely deterministic. So I couple it with a source of quantum noise, and which you can't say that the experiment is irrelevant. I write an app on my phone that flips a quantum mechanical coin, and use it to make daily decisions. At some point, the phone will make some sort of decision that will either increase or decrease my lifespan.

Uh, what?

If you say that Fred would have to be insane to do X, Y, and Z, you are making statements about Fred assuming that Fred has pseudo-human motivations, at which people you are using the thought processes that theologians use to make statements about what Fred will do or what Fred won't do.

This kind of objection doesn't make any sense. Probabilities within MWI strictly adhere to the Born Rule, so even if you can suppose that some seemingly weird thing might exist, the probability of you finding yourself in that world is so unbelievably minuscule that it is irrelevant.

I'm not objecting. MWI implies that there is version of reality in which a mega-intelligence has created a uber-version of Disneyland. That doesn't particularly bother me.

Personally, I think it would be cool if MWI was right and there are parallel universes. I've got a lot of questions about the universe, and I'm looking forward to meeting Fred.

Richard Dawkins might not like some of the implications but that's his problem.

Finding yourself in a highly improbable universe is not irrelevant if in the other universes you don't exist at all. That's the whole point of the anthropic principle. If may be highly improbable that after you die you end up in some sort of mega-Disneyland (if you've been good), but if you run the numbers, I don't think that it's that much less likely than the odds that you were born in the first place.

Also, I'm showing a bit of my inner crackpot here. He looks and sounds a lot like Frank Tipler, and I keep my inner crackpot under control by telling it that all he has to do is to wait a few decades and see what happens.

 

[stefanbanev]

If what we call dark matter is normal matter that exists in 100 different universes then it should not be expected to interact very strongly with itself. For 2 particles to collide they would have to be in the same universe and with 100 different universes there is only a 1% chance of that. I don't know how weakly dark matter interacts with itself but you can pick a number of universes to match whatever level of interaction there is.

It makes sense for me and it may be a verifiable idea; the number of contributing universes should be huge so, according to this idea dark matter should not manifest interaction at all if the event in our universe is low probable event so in majority other universes such event did not take place or has a wide range of different patterns. One problem, it is tricky to find the low probable event at cosmic scale ;o)

 

[DavidMcC]

...
Your parallel universe idea basically requires the existence of dark matter anyway yet with the added complexity of being in another universe.

But that is nothing in comparison with the added complexity of making the "one universe" cosmology fit with the rest of astronomical and cosmological data, such as lop-sided particle-physics laws, dark energy that implies that the cosmological constant isn't even constant, etc, etc, not to mention the non-discovery of dark-matter particles.

 

[Chalnoth]

But that is nothing in comparison with the added complexity of making the "one universe" cosmology fit with the rest of astronomical and cosmological data, such as lop-sided particle-physics laws, dark energy that implies that the cosmological constant isn't even constant, etc, etc, not to mention the non-discovery of dark-matter particles.

What are you going on about? There is no evidence as of yet that the cosmological constant isn't constant, and dark matter is expected to be extremely hard to detect, so it's hardly a surprise we haven't yet.

 

[Cosmo Novice]

But that is nothing in comparison with the added complexity of making the "one universe" cosmology fit with the rest of astronomical and cosmological data, such as lop-sided particle-physics laws, dark energy that implies that the cosmological constant isn't even constant, etc, etc, not to mention the non-discovery of dark-matter particles.

I was under the impression the cosmoloigcal contant is theoretically constant. It is not temporally constant (ie: it changes over time) but is spatially constant.

 

[twofish-quant]

But that is nothing in comparison with the added complexity of making the "one universe" cosmology fit with the rest of astronomical and cosmological data, such as lop-sided particle-physics laws, dark energy that implies that the cosmological constant isn't even constant, etc, etc, not to mention the non-discovery of dark-matter particles.

I strongly suspect that this isn't the case, and if you get a multiple universe theory to the point where you can fit the data, then it will be as complex if not more complex than what we have now. If you have a complex theory, then adding universes to the theory makes things more complex and not less complex.

I'd be interested in hearing why you would think otherwise.

 

[Misericorde]

How can a multiple universe theory of dark matter POSSIBLY be LESS complex? You'll need to include all of the elements of the a one-universe cosmology, and in addition you have to figure out how two spatially and temporally separated bubbles interact in what seems like a pretty uniform manner. Seems a bit mad to me as a matter of fact, and again, against the spirit of a multiverse if not every possible practice of one.